On the eve of the Knicks’ season opener, the NBA said it is investigating reported allegations team brass staged illegal workouts with draft prospects, including Wilson Chandler, across the past four years — a probe centering on East Coast scout Rodney Heard and senior VP Glen Grunwald. Both are Thomas hires who still work for the club.

If found guilty, the Knicks could face fines, suspensions — and at its harshest — loss of a future draft pick. It also could put the status of Heard and — more importantly — Grunwald into question. Team president Donnie Walsh admits he has looked to hire Chris Mullin as general manager but says he does not have a opening because of Grunwald’s spot.

If the NBA finds allegations true, it also could mean Thomas’ chances of rejoining the Knicks in a prominent role will be compromised. Some of the alleged violations also occurred during Walsh’s watch.

According to a Yahoo! Sports report, during the Thomas era, Heard staged allegedly improper workouts in Atlanta with Brandon Rush and Chandler in 2007 weeks before the pre-draft camp in late May. Teams cannot stage workouts with college players until after the pre-draft camp.

An NBA spokesman said in an e-mail, “We will be investigating these allegations.”

Contacted by The Post, Heard last night referred phone calls to top Knicks management.

The Knicks could face the severest penalty if they had improper contact with Chandler, because they wound up taking him 23rd in the 2007 Draft under odd circumstances. Chandler did not work out for other teams and The Post confirmed he was given a guarantee at some point before the draft. No formal workout between the Knicks and Chandler was ever announced to the media.

Agent Chris Luchey represents several of the players named, including Chandler, and is said to be close with Heard. He did not return calls from The Post.

Thomas hired Heard in 2006 from the Hawks. The 2007 Draft was run by Grunwald. Heard and Grunwald still are close to Thomas. Heard denied in the report he was present at the Rush workout, during which the player tore his ACL.

Also mentioned was a 2009 workout with Dar Tucker of DePaul during Walsh’s first draft that allegedly was illegal because it featured two sessions in one day, deemed against bylaws. Tucker was quoted as saying multiple players were worked out in two-a-day sessions.

The Knicks released a statement, saying, “The NBA is looking into the matter and we will fully cooperate and defer all comment to them.”

Walsh did not return calls and distanced himself from the charges, reportedly saying, “I don’t know anything about this. I didn’t know any of our scouts worked out people like this. They know they’re not supposed to.”

The report stated other players before this year’s draft, including Baylor’s Ekpe Udoh and Notre Dame’s Tory Jackson, might have been put through more workouts than the Knicks were permitted under bylaws.